This method is based on the principle that the flow of blood through the lungs (pulmonary blood flow) is proportional to the rate at which a gas that is soluble in the blood and absorbed through the alveoli by respiration is flushed out.
pulmonary shunt
If the patient has an intrapulmonary shunt, the percentage shunt flow is calculated according to Fick's principle for oxygen, expressed in %, and the pulmonary blood flow is corrected to the cardiac time volume (CVV).
HZV measurement in Innocor®
The HZV measurement in Innocor is the further development of a gas analyzer developed for space research for the measurement of the pulmonary gas exchange medium of a mass spectrometer (Amis 2000). Innocor uses photoacoustic spectroscopy (PAS) for the gas analysis, which has been specially developed and patented for this purpose, which measures extremely accurately and is stable over a long period of time. This makes the IGR method with Innocor very simple and absolutely user-friendly to use in the daily routine, for non-invasive measurement of HZV at rest and under stress.
Measurement procedure
The patient first inhales room air. The ergo-spirometric parameters are measured, displayed and stored “breath by breath”. For the HZV measurement, a rebreathing valve automatically switches from room air breathing to ventilation with a breathing bag. The bag contains a gas mixture consisting of 90% room air enriched with 9.4% oxygen and the inert gases SF6 (0.1%, insoluble in blood) and nitrous oxide (0.5%, soluble in blood). The two inert gases are continuously measured using photoacoustic spectroscopy (PAS). The patient's CO2 level remains at a consistently low level during rebreathing from the bag, thanks to the oxygen supply. After 4 to 5 breaths from the bag, the rebreathing valve switches back to room air breathing and continues to measure the ergo-spirometric parameters “breath-by-breath”. The times for the HZV measurement can be integrated into the load protocol as desired or activated manually (e.g. for peak measurements).
